This invention relates, in general, to hybrids, and more specifically, to broadband 180 degree hybrids.
Broadband 180 degree hybrids are commonly used in many analog and RF/microwave components. Such hybrids form basic building blocks in constructing components including balanced mixers, balanced amplifiers for improved second order IMD (intermodulation distortion) performance, and general networks which transition power from a balanced to an unbalanced condition as used in antennas.
Most broad bandwidth hybrids (on the order of an octave or greater) are constructed using either ferrite material or transmission lines. Ferrite hybrids, constructed of toroidal ferrite, are generally used in frequencies below 500 MHz. As frequencies increase, ferrite hybrids experience a decrease in Q value. Transmission line construction is favored for high frequencies due to the high Q which transmission lines exhibit. The transmission lines operate as broadside coupled lines on suspended substrata.
While both types of 180 degree hybrids are widely used, neither is compatible with MMIC (monolithic microwave integrated circuit) technology. MMIC circuits favor lumped or semi-lumped networks of capacitors, inductors, resistors, and, in some cases, short transmission lines. Although some MMIC circuits have been constructed using lumped or semi-lumped elements, such circuits have almost invariably been limited to narrow bandwidths of around 10 to 20% of the center frequency or fractional bandwidth.